Charge time start control for interconnect PABX

ABSTRACT

In an interconnect .[.PABX.]., .Iadd.telephone equipment .Iaddend.which does not have an answer signal returned thereto, decision logic makes use of returned audible busy and ring-back signals to determine if a connection extended through a telephone utility network to a called station is completed.

This invention relates to interconnect private automatic branchexchanges (PABX) and, more particularly, to an improved technique fordetermining whether or not connections extended from calling stations ofan interconnect PABX through a telephone utility network to calledstations have been completed.

For many years in the past, substantially all telephone facilities(including a PABX) situated on the premises of a subscriber of atelephone utility were provided by and were under the control of thetelephone utility. In this case, charges for metered local calls and/orlong-distance for toll calls made from any calling station of atelephone subscriber is determined by the telephone utility using solelytelephone utility equipment.

In some cases, it is desirable to individually bill a user who uses acalling station of a PABX who makes a call through the telephone utilitynetwork to a called station, rather than to merely to be able to billthe PABX subscriber. One obvious example of such a case is that of ahotel or motel PABX, in which it is essential that the individual hotelor motel guest be billed. Another example is a business organizationwith different profit/loss centers. Telephone utilities have developed,for their own use, telephone systems capable of metering local callsand/or charging for long-distance toll calls made from calling stationsof such a PABX. By way of examples, such PABX billing telephone systemsare disclosed in U.S. Pat. No. 3,721,769, which issued on Mar. 20, 1973to Krock et al. (which is assigned to GTE Automatic ElectricLaboratories Inc.) and in U.S. Pat. No. 4,090,034, which issued May 16,1978 to Moylin (which is assigned to Bell Telephone Laboratories).

As known in the telephone art, there are several well known audiblesignals which are returned to the calling-station user. These audiblesignals include, among others, dial tone, all-trunks busy,called-station busy and ring-back. Each of these audible signals isdistinctive and its call-status meaning is well known and easilyrecognized by calling-station telephone users. However, not all types ofcall-status signals are returned to the user of a calling telephonestation. For instance, when a telephone connection is extended from acalling station through a telephone utility network to a called station,the called station, on going off-hook, returns an answer signal(commonly known as answer supervision) to the telephone utility network.This answer signal, which is a call-station signal indicative of acompleted extended connection to the called station, is available to thetelephone utility for determining the start of the time-charge periodfor either a metered local call or a long-distance toll call made from acalling station of a calling subscriber. However, this answer signal,which is returned from a called station to the telephone utilitynetwork, is not commonly further returned or made available by thetelephone utility network to any of the equipment (including a PABX)situated at the calling subscriber's premises.

As long as the telephone utility network is the provider of a telephonesubscriber's PABX, it is not essential that the answer signal returnedto the telephone utility network be further returned to the PABX(although it might be less costly if the answer signal were available atthe PABX). However, recently telephone subscribers have been installingon their premises so-called interconnect telephone equipment which isnot furnished by the telephone utility. In the case of an interconnectPABX, no answer signal is returned to the interconnect PABX in responseto the completion of the extension of a connection from a callingstation of the PABX through the telephone utility network to a calledstation. How, then, can the possessor of an interconnect PABX (e.g.,hotel or motel operator, a business owner, etc.) determine the propercharge time period for a metered local call or a long-distance toll callmade by a user (hotel or motel guest, business employee, etc.) of acalling station of the interconnect PABX through the telephone networkto a called station?

Currently, the answer to this question is to make a tentative assumptionthat the extension of a connection, from an interconnect PABX callingstation through the telephone utility network to a called station, iscompleted, so that in all cases a charging time period is started. Ifthe charging time period starts a given few seconds following thedialing of the last digit by the calling station and lasts apredetermined short interval (e.g., 20 seconds) without the callingstation going on-hook, the tentative assumption is made permanent and acharge for the metered or long-distance toll call is made to the user ofthe calling station of the interconnect PABX. However, if the callingstation goes on-hook within the short interval (e.g., 20 seconds), thetentative assumption that the extended connection has been completed isreversed and the charge time period therefor is cancelled.

While statistically this current solution is reasonably accurate, it isplain that there are occasions when (A) charges are made for telephonecalls in which the extension of connection to the called station hasnever been completed (e.g., whenever a calling station user staysoff-hook for more than 20 seconds despite the fact that a busy signal ora ring-back signal is returned continually during the entire interval inwhich the calling station user is in an off-hook condition), and (B) nocharge is made to a calling station user of the interconnect PABX whenthe total time for the completion of the completed extended connectionplus the conversation time period is less than the predeterminedinterval (e.g., less than 20 seconds). This is particularly a problemwhere short data calls may be made, information exchange performed andthe call terminated (e.g. credit verification).

The present invention is directed to an improved technique available atthe interconnect PABX for more accurately determining whether or not aconnection extended from a calling station of the interconnect PABXthrough a telephone utility network to a called station has beencompleted, despite the fact that no answer signal is returned from thecalled station to the interconnect PABX in response to the completion ofthe extension of a connection thereto. More specifically, in accordancewith principles of the present invention, improved apparatus formingpart of the interconnect PABX decides whether or not an extendedconnection through the telephone utility network to the called stationhas been completed. The improved apparatus comprises a busy signaldetector for deriving a first output in response to a return of anaudible busy signal; a ring-back signal detector for deriving a secondoutput in response to a return of an audible ring-back signal; switchmeans for deriving a third output indicative of whether a callingstation of the interconnect PABX is in an off-hook condition or is in anon-hook condition; and connection complete or incomplete decision logicmeans having the first, second and third outputs applied as respectiveinputs thereto for (1) deriving a first control signal indicative of anincomplete extended connection in response to either (a) the indicationby said first output of the existence of an audible busy signal or (b)the indication by the second and third outputs of the occurrence of acalling station on-hook condition that occurs at the end of a callingstation off-hook condition interval during which an audible ring-backsignal occurs and thereafter continues to occur until the end of theinterval, and for (2) deriving a second control signal indicative of acomplete extended connection in response to an audible ring-back signalthat occurs during the interval, but which terminates prior to the endof the interval, so that the calling station remains in an off-hookcondition for a period of time after the audible ring-back signal hasterminated.

In the drawings:

FIG. 1 is a block diagram illustrating the relationship among aninterconnect (non-telephone utility) PABX, a telephone utility networkand a called station that is not part of the aforesaid interconnect PABX(but which may or may not be part of another interconnect ornon-interconnect PABX);

FIG. 2 is a functional block diagram of one typical embodiment of aninterconnect PABX, and

FIG. 3 illustrates a block diagram of charge-timing-period start-controlapparatus incorporating the principles of the present invention.

Referring to FIG. 1, there is shown in block diagram interconnect(non-telephone utility) PABX 100, telephone utility network 102 andcalled station 104 to which a connection may be extended from a callingstation of PABX 100 through telephone utility network 102. Morespecifically, interconnect PABX 100, in response to the dialing of apredetermined access digit by a calling station thereof, extends aconnection over a telephone line 106 from that calling station of PABX100 to telephone utility network 102. As is usual, telephone utilitynetwork 102 returns a dial tone over telephone line 106 to the callingstation of PABX. The calling station which may be either a rotary dialtelephone or a push-button dial telephone) forwards connection-extendingdialed digit signals over telephone line 106 to telephone utilitynetwork 102. Telephone utility network 102, in response to these dialeddigit signals, extends a connection over telephone line 108 to a calledstation 104 (which called station may be anywhere in the world and mayor may not be part of another PABX). Should any of the facilities oftelephone utility network 102 be busy or should called station 104itself be busy, telephone utility network 102 returns an audibleall-trunks busy signal or an audible called-station busy signal overtelephone line 106 to PABX 100. Assuming that neither telephone utilitynetwork 102 or called station 104 is busy, telephone utility network 102forwards a ring signal to called station 104 over telephone line 108,while, at the same time, returning an audible ring-back signal overtelephone line 106 to PABX 100. Should called station 104 be answered(i.e., go off-hook), an answer signal is returned to telephone utilitynetwork 102 over telephone line 108. However, telephone utility network102 does not further return an answer signal over telephone line 106 toPABX 100. Thus, in summary, the only control signals returned bytelephone utility network 102 to PABX 100, in response to making a callto called station 104 are those that can be returned over an audibleconnecting path, such as dial tone, an audible busy signal and anaudible ring-back signal.

FIG. 2 is a functional block diagram of one typical embodiment ofinterconnect PABX 100. PABX 100 includes a plurality of telephonestations 200-1 . . . 200-N (where N is a plural integer). Each oftelephone stations 200-1 . . . 200-N can comprise a standard dialtelephone, or, alternatively, some other type of terminal equipment,such as a teletype, a data phone, an on-line computer, etc. In anyevent, telephone stations 200-1 . . . 200-N are associated withswitching means 202. Also associated with switching means 202 is signaldetectors and controller 204. Signal detectors and controller 204 hasaccess to station message detail recording means 206. As usual in aPABX, any one calling one of telephone stations 200-1 . . . 200-N canextend a connection through switching means 202 to any called one oftelephone stations 200-1 . . . 200-N by dialing the extension number ofthe called station of PABX 100. In response to this dialing, switchingmeans 202 is operated by the controller of block 204 to extend theconnection to the called telephone station 200-1 . . . 200-N of PABX100. Should any one calling one of telephone stations 200-1 . . . 200-Ndesire to extend a call connection through telephone utility network102, a predetermined access digit is dialed, which causes switchingmeans 202 to be operated by the controller 204 to extend a connection totelephone utility network 102 from that calling one of telephonestations 200-1 . . . 200-N through telephone line 106. Block 204includes signal detectors for selectively detecting various audiblesignals forwarded thereto through switching means 202 from telephonestations 200-1 . . . 200-N and also from telephone utility newtwork 102over telephone line 106. These audible signal detectors may includeaudible dialed digit signals (in the case of PABX push-button dialtelephones), but always include audible busy signal and ring-back signaldetectors. Also included in block 204 are signal detectors for detectingthe on-hook/off-hook condition of each of telephone stations 200-1 . . .200-N.

Block 204 in combination with block 206, includes means for determiningand recording information required to charge an individual user of PABX100 for metered local calls and/or long-distance toll calls extendedthrough telephone utility network 102. In some cases (such as in thecase of a hotel or motel PABX) each of telephone stations 200-1 . . .200-N is assumed to be a user. In other cases (such as in the case of abusiness PABX) the user (such as an employee) may have a personalidentification number which is dialed by him whenever he makes a chargecall from any one of calling stations 200-1 . . . 200-N. In any event,information required to charge for a call includes the charge timeperiod of the call (i.e., the portion of the calling-station off-hookinterval that extends from the start of charging for a call until thecalling-station goes on-hook) and, in the case of a long-distance tollcall, the area and office codes of the called station. Block 204 and/orblock 206 contain conventional toll-ticketing equipment for measuringthe length of the charge time period, determining the charge rate for atoll call and recording in station message detail recording means 206details of each charged telephone call. These details also can includethe time of day, the dialing number of the called station, total numberof called facilities used, etc.

PABX equipment for performing the functions so far described forinterconnect PABX 100 of FIG. 2 is well known in the art and includesthe PABX equipment disclosed in each of the aforesaid U.S. Pat. Nos.3,721,769 and 4,090,034. What makes interconnect PABX 100 different fromthe telephone-utility provided PABX equipment of the prior art is thatinterconnect PABX 100 has no way of ever having returned thereto answersignal information (as do some of the telephone-utility provided PABXequipments of the prior art) for determining the occurrence of the startof a charge time period. In order to accomplish this function, signaldetectors and controller 204 of interconnect PABX 100 includes thecharge-timing-period start-control apparatus shown in block diagram formin FIG. 3.

Referring to FIG. 3 there is shown ring-back signal detector 300 andbusy signal detector 302, which respond, respectively, to an audiblering-back signal and to an audible busy signal returned from telephoneutility network 102 over telephone line 106 (which audible signals areforwarded by switching means 202 to block 204). Ring-back signaldetector 300, in response to the detection of an audible ring-backsignal, provides a first output which is applied as a first input tocall complete or incomplete decision logic 304. Busy signal detector302, in response to the detection of an audible busy signal, provides asecond output which is applied as second input to call complete orincomplete decision logic 304. On/off-hook switch 306 produces a thirdoutput indicative of the on-hook or the off-hook condition of theparticular calling station of PABX 100 attempting to extend a connectionthrough telephone utility network 102 to a called-station 104. The thirdoutput from on/off-hook switch 306 is applied as a third input to callcomplete or incomplete decision logic 304. Call complete or incompletedecision logic 304 can take the form of a hard-wired logic circuit or,alternatively, it can take the form of a software programmed signalprocessor. In any event, call complete or incomplete decision logic isselectively responsive to the respective first, second and third inputsthereto from ring-back signal detector 300, busy signal detector 302 andon/off-hook switch 306 to logically decide either a first control output308 therefrom indicative of "no charge" or a second control output 310therefrom indicative of "start-call timing." A logical relationshipbetween the respective "no charge" and "start call timing" outputs fromcall complete or incomplete decision logic 304 and the condition of eachof the respective first, second and third inputs thereto is shown in thefollowing table:

                  TABLE I                                                         ______________________________________                                               Condition        Output                                                ______________________________________                                        1        Busy signal detected                                                                             No-charge                                         2        Ring-back signal   No-charge                                                  detected continually                                                          until "on-hook" occurs                                               3        Ring-back signal   Start call                                                 detected followed by a                                                                           timing (upon                                               termination of ring-back                                                                         ring-back                                                  signal while "off-hook"                                                                          termination)                                               remains                                                              ______________________________________                                    

Despite the fact that the interconnect PABX 100 never has an answersignal returned to it from telephone utility network 102, it can be seenfrom the above table that call complete or incomplete decision logic 304is able to make use of the audible ring-back signal or the audible busysignal (which are returned to PABX 100 from the telephone utilitynetwork 102) in a logical manner to determine quite accurately (i.e., onthe basis of very good circumstantial evidence) whether or not theextended connection through telephone utility network 102 to a calledstation has, in fact, been completed. This, in turn, permits the startof timing for charging purposes to be determined much more accuratelythan was heretofore possible in the case of an interconnect PABX, whichdoes not have available to it the actual answer signal returned from thecalled-station.

What is claimed is:
 1. In an interconnect PABX which includes meanscapable of (A) extending a telephone connection from respective callingtelephone stations of said interconnect PABX through a telephone utilitynetwork to respective called telephone stations, (B) receiving areturned audible busy signal in response to either said network or acalled station being busy, and (C) receiving a returned audiblering-back signal when a called station is ringing; an answer signalreturned by a called station to said network in response to that calledstation going off-hook being unavailable to said interconnect PABX, saidanswer signal being indicative of the extended telephone connection tothat called station being completed; improved apparatus forming part ofsaid interconnect PABX for deciding whether or not an extendedconnection through said telephone network to a called station has beencompleted, said apparatus comprising:a busy signal detector for derivinga first output in response to a return of said audible busy signal; aring-back signal detector for deriving a second output in response to areturn of said audible ring-back signal; switch means for deriving athird output indicative of whether a calling station of saidinterconnect PABX is in an off-hook condition or is in an on-hookcondition; and connection complete or incomplete decision logic meanshaving said first, second and third outputs applied as respective inputsthereto for (1) deriving a first signal indicative of an incompleteextended connection in response to either (a) the indication by saidfirst output of the existence of an audible busy signal or (b) theindication by said second and third outputs of the occurrence of acalling-station on-hook condition that occurs at the end of acalling-station off-hook condition interval during which an audiblering-back signal occurs and thereafter, continues to occur until saidend of said interval, and for (2) deriving a second control signalindicative of a complete extended connection in response to an audiblering-back signal that occurs during said interval, but which terminatesprior to said end of said interval, so that the calling station remainsin an off-hook condition for a period of time after the audiblering-back signal has terminated.
 2. In said interconnect PABX defined inclaim 1, which further includes a station message detail record meansfor recording toll charges of toll telephone calls extended from acalling station of said interconnect PABX through said telephone utilitynetwork to called stations in accordance with the area and office codesof any particular called station and the duration of a time period of atoll telephone call from a particular interconnect PABX calling stationand that particular called station; andwherein said station messagedetail record means is coupled to said improved apparatus and isresponsive to the occurrence of said second control signal for startingsaid time period and is responsive to said particular calling stationgoing into an on-hook condition at the end of said interval for endingsaid time period. .Iadd.
 3. In interconnect telephone equipment whichincludes means capable of (A) extending a telephone connection from acalling telephone station of said interconnect telephone equipmentthrough a telephone utility network to respective called telephonestations, (B) receiving a returned audible busy signal in response toeither said network or a called station being busy, and (C) receiving areturned audible ring-back signal when a called station is ringing; ananswer signal returned by a called station to said network in responseto that called station going off-hook being unavailable to saidinterconnect telephone equipment, said answer signal being indicative ofthe extended telephone connection to that called station beingcompleted; improved apparatus forming part of said interconnecttelephone equipment for deciding whether or not an extended connectionthrough said telephone network to a called station has been completed,said apparatus comprising:a busy signal detector for deriving a firstoutput in response to a return of said audible busy signal; a ring-backsignal detector for deriving a second output in response to a return ofsaid audible ringback signal; switch means for deriving a third outputindicative of whether a calling station of said interconnect telephoneequipment is in an off-hook condition or is in an on-hook condition; andconnection complete or incomplete decision logic means having saidfirst, second and third outputs applied as respective inputs thereto for(1) deriving a first signal indicative of an incomplete extendedconnection in response to either (a) the indication by said first outputof the existence of an audible busy signal or (b) the indication by saidsecond and third outputs of the occurrence of a calling-station on-hookcondition that occurs at the end of a calling-station off-hook conditioninterval during which an audible ring-back signal occurs and thereafter,continues to occur until said end of said interval, and for (2) derivinga second control signal indicative of a complete extended connection inresponse to an audible ring-back signal that occurs during saidinterval, but which terminates prior to said end of said interval, sothat the calling station remains in an off-hook condition for a periodof time after the audible ring-back signal has terminated. .Iaddend.